Electrical stop mechanism



Nov. 7, 1944. E. E. GARRETT ELECTRICAL STOP MECHANISM Filed Sept. 17,1942 ATTORNEY w M RR OR A mm 4, mm A (h .E a; W a p E ,2. a S u n ml loN. 2 Mm m m m I G. 1 mN .WON 7 0v mm RN m Q20 ON mm E m \J Tl-.. EM- y/N a 1. 31:1 QM L m R x t 3 mm. n 8 Q 3 B a N Patented Nov. 7, 19442,362,197 ELECTRICAL s'ror MECHANISM Elmer E. Garrett, Rockville,Centre, N. Y., assignor to Ford Instrument Company, Inc., Long IslandCity, N. Y., a corporation of New York Application September 17, 1942,Serial No. 458,705

12 Claims.

I This invention relates to stop devices to limit the extent of motionof a movable member and particularly to such devices which operate tointerrupt the power which drives the movable member.

When the movable member has considerable mass it will move under itsinertia after the propelling power is cut oil a distance depending uponits speed and a characteristic of this invention is the fact that thetime of cut-off is advanced with respect to the limit of movement anamount proportional to the speed.

For this purpose under the invention a drag device operated by the powermotor develops an output torque proportional to the operating speed andthis variable torque is used to interrupt the power according toconditions. Specifically the power device is electrically operated and acon-. tact in the circuit is biased to closed position, but this biasingforce is opposed by the torque of the drag device, and as the movablemember comes within a predetermined distance of the absolute limit ofits movement it sets into operation a cause that progressively weakensthe biasing force until the torque of the drag device is suiiicient toovercome the residual biasing force and open the contact.

For practical purposes the power means must be reversible so as toactuate the movable member in either direction and there is a circuitbreaking contact in each directional circuit. These are mounted onpivoted arms the adjacent ends of which are connected by a spring thatholds the contacts closed. Centering springs are attached to theopposite ends of the arms and have their inner ends attached to amovable post between the arms. These centering springs are weaker thanthe holding spring and normally exert little opposition torque. As thepost is moved however one way or the other the torque of one of thecentering springs is increased and to that extent neutralizes. thetorque of the holding spring.

The output of the drag device has a torque member engageable with thearms in a direction to supplement the torque of the centering springs asthe post is displaced. The greater the output torque, that is, thegreater the speed, the sooner is the torque of the holding springovercome and the circuit broken.

A mechanical member that may be termed a movement measuring device isdriven proportionately to the movable member and it becomes effectivenear the limit of movement in both directions to move the post with itandthus begin to store up energy in one of the centering springs. Themechanical member also operates a projection at the limit of itsmovement that engases the contact arm and breaks the contact if theopening torque produced by the drag device and the centering spring hasnot overcome the bias of the holding spring.

The invention also includes means to decelerate the movable member. Inthe preferred construction this includes means to reverse theenergization of the power means and thus brake its movement. The Contactarms on their opposite ends carry normally open contacts that areconnected in circuit with the power means reversely to that of thenormally closed contacts on the respective arms. The torque inopposition to the holding spring therefore first moves the contact armto open the circuit that controls the power device in the direction inwhich it is operating, and further movement of the Contact arm willenergize the power device in the opposite direction so that theresulting deceleration will be such as to maintain a balance between thetorque of the holding spring and the combined torques of the output ofthe drag device and of the centering spring.

The drawing is a schematic showing of one way in which the invention maybe embodied, but it will be understood that this is only intended toillustrate the principles involved and that the mechanical embodiment ofthose principles will accord with individual discretion.

The drawing shows a follow-up or motion reproducing mechanism in which aservomotor supplies the power for the driven member. Other poweramplifying means may of course be employed, such as a magnetic clutch ofknown form operated by reversely energizable coils.

The input or primary movement is shown as introduced manually by a crankl and fed into one side of a differential 2. the other side being gearedto the output shaft 3 or servomotor l. The output I of the differentialtherefore represents the diiierence between the input and the response.

The motor is energized in one direction or the other, depending upon theposition of contacts, by a source 6 of electric power. The usual relaycontacts are operated by the diiierential output 5, and consist ofcenter movable contacts 1 and the fixed contacts la and lb connected incircuit, respectively, with leads 8 and 9 and, through other contacts tobe described, with motor terminals I0 and II, respectively. The commonterminal I! is connected to one side of the power source 6 the otherside of which is connected by lead l3 with arm N that carries thecontacts I.

The motor 4 is assumed to have a split field winding so that connectionof the source 8 with the terminals Ill and II will energize the motor inrelatively opposite directions. The leads 8 and 9 are connectible withthese terminals through contacts that operate as circuit breakers andare automatically controlled in accordance pair of contacts and closethe other.

with the position and speed of the'follower member.

Two contact arms I! and ii are pivotally mounted on a fixed support I.Each of these arms carries two contacts, one on each side of the pivot,that coast with fixed contacts carried by the support H, the contactsbeing disposed so that rotation of an arm tends to open one Lead 8connects with movable stop contact Ida on arm i5 that coacts with fixedcontact ilb connected by lead 18 with terminal ill. Lead 8 connects withmovable stop contact 20a on arm ii that coacts with fixed contact 20bconnected by lead 2i with terminal ii. A spring 22 connects the two endsof the arms and exerts a torque that reduction gearing 82, shaft 34 andpinion ll. This member II is loosely mounted on shaft 8| that will laterbe referred to, and is adjacent and opposes a stop disc 21 also looselymounted on shaft 28 and carrying the post 20. The stop disc 31 has anabutment II that is disposed in urges both movable contacts Ila and a toclosed position.

On the opposite side of its pivot arm 15 carries movable contact 23athat coacts with fixed contact 2317, and similarly on its opposite endarm I6 carries contact 24a that coacts with fixed con- .tact 24b. Spring22 biases these contacts to open in alternative energizing circuits. Oneside of the power source 8 is connected by lead 25 to the fixed contacts23b and 24b, while the movable contacts are connected with the motorterminals, lead 26 connecting contact 23a with lead 21 and hence withterminal II, and lead 21 connecting contact 24a with lead 19 and hencewith terminal l0. Thus it will be seen that the circuits including thesedecelerating contacts are independent of the follow-up or relay contactsI, la and lb, and are made only when the follow-up circuits are open.

Turn now to the means for actuating the contact arms i5 and I6. Opposingthe holding spring 22 are centralizing springs 28 and 29 that areanchored at their inner ends to a post In between the arms and at theirouter ends to the ends of the respective arms. The post is movable andis normally held central by the springs. The springs are under little orno tension when the post is centralized and they are weaker than theholding spring 22 so that as the post is moved one way or the other andplaces one of the centralizing springs under tension, the counter torquethus produced is not sumcient to overcome the torque of the spring 22. Asupplemental torque must be produced to combine with that of thecentralizing spring in order to open the circuit breaking contacts, andin order that the breaking of the motor circuit may be advancedaccording to the speed, the supplemental torque producing means is maderesponsive to the speed of the follower member. This supplemental torquewill not alone be sufficient to open the motor circuit at the maximumspeed of the follower and it is necessary for the torque of thecentralizing spring also to be present to overcome the torque of thespring 22. Therefore the post lil remains central until a predetermineddistance before the follower reaches the limit of its movement when amember moved with the follower contacts the post support and causes thepost to move along. This will now be described.

A motion measuring member 3|, shown as a geared disc, is driven at areduced rate by output shaft 2 of motor 4 through countershaft 22,

the path of an abutment 20 on the member ll. Therefore the member II canmake a rotation of nearly 360 from one abutment contact position to theother. The disc I! also carries a striker member ll that is located tostrike the arms ii and II adjacent the spring 22 and is positionedmidway between them when the disc is centralized by the springs 2| and2|. A sufficient movement of the disc I! therefore will positively openeither contact l8aor 200, depending upon which way the disc is moved.

The speed responsivedevice consists of a drag member I that may be ofany known construction suitable for the purpose, such as a magnetic dragor a viscous drag. The housing or rotor is geared to the shaft 22 so asto be driven at a speed proportional to that of the output 3, and thedrag element is on the shaft 36. This shaft will therefore be biased bya torque proportional to the speed of the rotor. The shaft extendsthrough a bearing in the fixed support I1 midway between the pivots forthe arms II and I0 and has on its end a T-shaped lever 42 the ends ofwhich are positioned to engage projections Ila and lie, on therespective arms. Therefore the member 42 will exert a force upon one ofthese projections, depending upon which way the motor is turning,proportional to the speed of the follower member.

A primary movement in the direction of the arrow will close contacts 1,lb and energize the motor 4 in the direction indicated by the arrow onthe shaft 3 through contacts 20a, 20b, and the motor I will continue torun until its response equals the primary movement, when the shaft I andthe contacts will be on center position and the motor will bedeenergized. The faster the motor runs to keep up with the primarymovement the more torque is being exerted by the member 62 on theprojection lia. This alone however is not enough to overcome the closingtorque of the holding spring 22 and open the contact 20a. If thefollower member approaches sufficlently close to its limit of movementfor the abutment 20 to engage the abutment 38, the stop disc 31 will becaused to rotate in the direction indicated by the arrow and thus movethe post 30 away from the arm I and increase the tension on the spring2!. The torque produced by the spring 2! combined with that exerted bythe member 42 will overcome the torque of the spring 22 if the speed ofthe motor is at all considerable, and the faster the motor is runningthe less torque from the spring 20 and hence the less movement of thestop disc is required to open the motor circuit.

The desired characteristics of the stop are that when either stopcontact is opened the friction of the follower member will oppose theinertia so that the follower member will slow down at a rate to maintainthis balanced condition with the stop contacts Just opened. If thefollower member does not decelerate at the desired rate the excessivedrag effect on member 42 will cause the appropriate contact arm to movesufficiently to close its decelerating contact. As this further movementof the arm closes the decelerating contact the motor is reverselyenergized and the iollower member is forcibly decelerated at the desiredrate.

At very low speeds the drag has little eflect and the torque of thecentering spring is Ju t gufilcient to balance the torquqe oi theholding spring at the limit oi travel. At this point the member 40engages the contact arm, thus assuring positive control in arrestingmotion or the i'ollower member. I

It will be noted that since the torque exerted by the drag isproportional to the speed of the power means, the velocity of thefollower movement is proportional to the distance oi the driven memberfrom the limit oi. travel while the electrical stop is in control.

It is obvious that the invention may be variously otherwise embodied andthat changes may be made in the construction shown in the drawing andabove particularly described within the principle and scope oi theinvention as pointed out in the appended claims.

I claim:

1. An electrical limit stop mechanism comprising an electricallyoperated power device, a

driven member operated thereby, an energizing.

circuit for the power device including a movable contact, means normallybiasing the contact to closed position, mechanical means operated by thepower device for opening the contact at the limit of movement of thedriven member, and means responsive to the speed of the driven memberfor applying an opening force upon the movable contact.

2. An electrical limit stop mechanism comprising an electricallyoperated power device, a driven member operated thereby, an energizingcircuit for the power device including a movable contact, means normallybiasing the contact to closed position, mechanical means operated by thepower device for opening the contact at the limit of movement of thedriven member, means actuated by the mechanical means for developing aforce in opposition to the biasing means before the limit of movement isreached, and means responsive to the speed of the driven member forapplying an opening force upon the movable contact, whereby the openingof the contact anticipates the limit of movement.

3. An electrical limit stop mechanism comprising an electricallyoperated power device including an output element driven thereby, anenergizing circuit for the power device including a movable contact, abiasing spring urging I the contact to closed position, a drag devicedriven by the output element and adapted to produce an output torqueproportional to the speed of the power device, and a torque elementoperated by the drag device and arranged to act upon the movable contactin opposition to the biasing spring.

4. An electrical limit stop mechanism comprising an electricallyoperated power device, an energizing circuit for the power deviceincluding a movable contact, a biasing spring urging the contact toclosed position, mechanical means operated by the power device foropening the contact at the limit of movement, a speed responsive dragdevice operated by the power device and arranged to apply its outputforce in opposition to the biasing spring, and means operated by themechanical means for supplementing the output force.

5. An electrical limit stop mechanism comprising an electricallyoperated power device, an energizing circuit for the power deviceincluding a movable contact, a biasing spring urging the contact toclosed position, mechanical means operated by the power device foropening the contact at the limit of movement, a, speed responsive dragdevice operated by the power device and arranged to apply itsoutputforce in opposition to the biasing spring, a second spring connected tosupplement the output force of the drag device and normally exertingless force than that oi the biasing spring, and means operated by themechanical means for increasing the tension of the second spring.

6. An electrical limit stop mechanism comprising an electricallyoperated power device, a driven member operated thereby, an energizingcircuit for the power device including a movable contact, a pivotedcontact arm carrying the movable contact, a biasing spring exerting aclosing torque on the arm, a second relatively weak spring connected atone end to the arm to exert an opening torque thereon, a movableattachment for the opposite end of the second spring, mechanical meansoperated by the power device for positively opening the contact at thelimit of movement of the driven member, speed responsive means operatedby the driven member for exerting an opening torque upon the contactarm, and means operated by the mechanical means for moving the movableattachment in a direction to increase the torque of the second spring.

7. An electrical limit stop mechanism comprising an electricallyoperated reversible power device, a driven member operated thereby,circuits for energizing the power device in respectively oppositedirections, a movable contact in each circuit, two pivoted contact arms,each carrying one of themovable contacts, a holding spring connectingthe two arms and biasing the contacts to closed position, a rotativedisc having a spring attaching post thereon, centering springs attachedat one end to the post and at their other ends to the respective contactarms in opposition to the holding spring, mechanical means operated bythe movable member adapted to engage the disc in advance of the limit ofmovement of the driven member and thereby increase the tension of one ofthe centering springs, and means actuated by the driven member andresponsive to the speed thereof for applying an opening torque to thecontact arm to which the said one centering spring is attached.

8. An electrical limit stop mechanism comprising an electricallyoperated reversible power device, a driven member operated thereby,circuits for energizing the power device in respectively oppositedirections, a movable contact in each circuit, two pivoted contact arms,each carrying one of the movable contacts, a holding spring connectingthe two arms and biasing the contacts to closed position, a rotativedisc having a spring attaching post thereon, centering springs attachedat one end to the post and at their other ends to the respective contactarms in opposition to the holding spring, mechanical means operated bythe movable member adapted to engage the disc in advance of the limit ofmovement of the driven member and thereby increase the tension of one ofthe centering springs, a drag device operated by the driven member andadapted to produce an output torque proportional to the speed of thedriven member, and a torque member operated by the output of the dragdevice and engageable with the contact arms in a direction respectivelyto supplement the opening torque of the centering springs.

9. An electrical limit stop mechanism comprising an electricallyoperated reversible power device, a driven member operated thereby,circuits for energizing the power device in respectively oppositedirections, a movable contact in each circuit, two pivoted contact arms,each carrying one of the movable contacts, a holding spring connectingthe two arms and biasing the contacts to closed position, a, rotativedisc having a spring attaching post thereon, centering springs attachedat one end to the post and at their other ends to the respective contactarms in opposition to the holding spring, mechanical means operated bythe movable member adapted to engage the disc in advance of the limit ofmovement of the driven member and thereby increase the tension of one oithe centering springs, a drag device operated by the driven member andadapted to produce an output torque proportional to the speed of thedriven member, a torque member operated by the output of the drag deviceand engageable with the contact arms in a direction respectively tosupplement the opening torque of the centering springs, and meansoperated by the disc for positively opening the contacts at the limit ofmovement of the driven member in its respective opposite directions.

10. In a motion reproducing mechanism including a primary movable memberthe motion of which is to be reproduced and a driven tollower member, anelectrically operated reversible power device connected to actuate thedriven member, circuits for energizing the power device in respectivelyopposite directions including reversing contacts operated by the primarymovable member, a movable contact in each circuit in series with one ofthe reversing contacts, a pivoted contact arm carrying each of saidmovable contacts, the two arms being juxtaposed, a holding springconnecting the adjacent ends the two arms and biasing the said seriescontacts to closed position, alternative energizing circuits for thepower device each including a movable contact on one of the arms soarranged as to be biased toward open position by the holding spring, thenormally open contact on each arm being connected to energize the powerdevice in the same direction as the normally closed series contact onthe other arm, a rotative disc having a spring attaching post thereon,centering springs attached at one end to the post and at their otherends to the respective contact arms in opposition to the holding spring,mechanical means operated by the movable member adapted to engage thedisc in advance of the limit of movement of the driven member andthereby increase the tension of one of the centering springs, and meansactuated by the driven member and responsive to the speed thereof forapplying a torque selectively to the arm to which the said centeringpring is attached supplemental to that of the centering spring and inopposition to that of the holding spring, thus tending first to open thenormally closed contact and then to close the normally open contact.

11. In a motion reproducing mechanism including a primary movable memberthe motion of which is to be reproduced and a driven follower member, anelectrically operated reversible power device connected to actuate thedriven member, circuits for energizing the power device in respectivelyopposite directions including reversing contacts operated by the primarymovable member, a movable contact in each circuit in series with one ofthe reversing contacts, a pivoted contact arm carrying each of saidmovable contacts, the two arms being juxtaposed, a holding springconnecting the adjacent ends of the two arms and biasing the said seriescontacts to closed position, alternative energizing circuits for thepower device each including a movable contact on one oi the arms soarranged as to be biased toward open position by the holding spring, thenormally open contact on each arm being connected to energize the powerdevice in the same direction as the normally closed series contact onthe other arm, a rotative disc having a spring attaching post thereon,centering springs attached at one end to the post and at their otherends to the respective contact arms in opposition to the holding spring,mechanical means operated by the movable member adapted to engage thedisc in advance of the limit of movement of the driven member andthereby increase the tension of one of the centering springs, a dragdevice operated by the driven member and adapted to produce an outputtorque proportional to the speed of the driven member, and a torquemember operated by the output of the drag device and engageable with thecontact arms in a direction respectively to supplement the torque of thecentering springs.

12. In a motion reproducing mechanism including a primary movable memberthe motion of which is to be reproduced and a driven follower member, anlectrically operated reversible power device connected to actuate thedriven member, circuits for energizing the power device in respectivelyopposite directions including reversing contacts operated by the primarymovable member, a movable contact in each circuit in series with one ofthe reversing contacts, a pivoted contact arm carrying each of saidmovable contacts, the two arms being juxtaposed, a holding springconnecting the adjacent ends of the two arms and biasing the said seriescontacts to closed position, alternative energizing circuits for thepower device each including a movable contact on one of the arms soarranged as to be biased toward open position by the holding spring, thenormally open contact on each arm being connected to energize the powerdevice in the same direction as the normally closed series contact onthe other arm, a rotative disc having a spring attaching post thereon,centering springs attached at one end to the post and at their otherends to the respective contact arms in opposition to the holding spring,mechanical means operated by the movable member adapted to engage thedisc in advance of the limit of movement of the driven member andthereby increase the tension of one of the centering springs, a dragdevice operated by the driven member and adapted to produce an outputtorque proportional to the speed of the driven member, a torque memberoperated by the output of the drag device and engageable with thecontact arms in a direction respectively to supplement the torque of thecentering springs, and means carried by the disc and operative to engagthe arms selectively and apply a positive torque thereto in oppositionto that of the holding spring.

EIMER E. GARRETT.

